This invention relates to a finisher for stacking sheets of paper or similar material moving in a predetermined direction in a specific alignment at a predetermined location and, more particularly, to a finisher for stacking sheets in which motion of each sheet is directed to two substantially perpendicular reference barriers defining a corner with a first edge of each sheet engaging the closer of the two reference barriers before a second edge of the sheet engages the other reference barrier.
Various arrangements have previously been suggested for sequentially aligning each sheet of paper or similar material forming a stack of sheets at a specific location on a support. This alignment of sheets in a stack has been utilized to enable stapling of a selected number of the sheets at a specific location on each stack of the stapled sheets, for example.
With imaging forming devices, particularly a printer or copier, for example, it is desired to be able to staple a predetermined number of sheets as they are fed separately from the image forming device. Each sheet is fed from the image forming device through exit corrugation rollers to a support surface. Each sheet falls by gravity onto a lower support surface for partial support thereby after exiting from the exit corrugation rollers with the remainder of the support of each sheet being by an output tray.
The number of sheets in each stack may be the same or different. Stapling may occur with some stacks of sheets but not others.
While each sheet falls in substantially the same predetermined location on the support surface or a top sheet supported on the support surface, they do not fall at exactly the same position. However, each sheet usually falls within a predetermined range in both its longitudinal and lateral directions.
Accordingly, each sheet must be quickly aligned with the other stacked sheets that are to be stapled together. Thus, it is desired to have a sheet aligning device capable of moving each sheet to a predetermined location.
This alignment must be accomplished in a very short period of time since a sheet moving device of the sheet aligning mechanism must complete alignment of the sheet before the next sheet arrives at the support surface. This time depends on the feed rate of the printed sheets but can be as small as one second, for example. Otherwise, the next sheet cannot fall within the predetermined range because of the presence of the sheet moving device of the sheet aligning mechanism.
Furthermore, a relatively complex sheet moving device must be employed if it is not disposed very close to the sheet on the support surface. However, if the sheet moving device is positioned in its home position very close to the sheet when it is disposed on the support surface, the sheet moving device of the sheet aligning mechanism must be moved out of the way before the next sheet falls towards the support surface by gravity and engagement of the sheet by a sheet engaging member of a bail actuator also falling by gravity.
An example of a previously suggested sheet aligning mechanism is shown and described in the aforesaid Ardery et al application, Ser. No. 09/793,360. It utilizes two fingers as the frictional moving member with each moving the sheet at a different portion of each cycle of operation.
The present invention uses a single frictional member to align a sheet at a predetermined location, which is a corner defined by two substantially perpendicular reference barriers although the two reference barriers do not have to intersect. Each of these two reference barriers is spaced a distance within a predetermined range from the position of an adjacent edge of the sheet supported by a lower support surface to which each sheet falls by gravity. One of the reference barriers is further from the adjacent edge of the sheet than the other reference barrier is from the edge of the sheet adjacent thereto when the sheet is disposed for support by the lower support surface after falling thereon by gravity.
The present invention uses a single aligning roller for having frictional contact with each sheet received by the support surface, which is preferably an upper surface of an accumulator table. The aligning roller continuously exerts a force on the sheet when it is in frictional contact with the sheet.
The aligning roller is aligned relative to each of the two substantially perpendicular reference barriers so that more of its force is applied to move the sheet toward the reference barrier spaced further from the adjacent edge of the sheet. This is accomplished by placing the aligning roller at angle greater than 45xc2x0 to the reference barrier spaced furthest from the adjacent edge of the sheet.
The direction of rotation of driving means, which rotates the aligning roller, is selected so that the force of the driving means tends to lift the aligning roller from the sheet being advanced. This limits the maximum alignment force on the sheet when the roller is subjected to a high resistive force from the sheet engaging a barrier or a load. This lifting action on the aligning roller reduces the normal force between the aligning roller and the sheet to decrease the alignment force, which is the product of the normal force and the coefficient of friction between the roller and the sheet, until a torque equilibrium state is reached.
An object of this invention is to provide a finisher having a single aligning roller for moving a sheet into engagement with two substantially perpendicular reference barriers, which define a corner, spaced different distances from adjacent edges of the sheet.
A further object of this invention is to provide a finisher in which aligned sheets in a stack can be stapled to each other.
Other objects of this invention will be readily perceived from the following description, claims, and drawings.